Method for wireless communication



Aug. 30, 1932. F SCHRTER 1,875,165

V METHD FOR WIRELESS COMMUNICATION Filed June 11, 1928 2 Sheets-Sheet 1 z scHReTER ATT NEY Aug. 30, 1932.

F. SCHRTER METHOD FOR WIRELESS COMMUNICATION Filed June 11, 1928 2 Sheets-Sheet 2 m17. scHaiTER A TORNEY Patented Aug. 30, 1932 i FRITZ scrrnTnn, or :BERLINQGERMANSL AssIGNon 'ro TELnFUNKnN GESELLSCIIAFT DRAIITLOSE TELEGRAPHIE 1W.l B. H.,

GERMANY Application i led .Tune 11,

In the practical application of wireless intelligence transmission on short waves ithas been found that at the receiving station one and the same signal comes in several times at short intervals of time. Such multiple' reception of one and the same signal, on the one hand, is due to the signal reaching the ref ceiving station not only in one direction, but also in the opposite direction around the earth, and, on the other hand, is due to the waves which carry the signal being able to pass around the earth several times. The sourceof disturbance first mentioned is remedied by providing either orboth the receiving and transmitting antennae with reflectors whereby radiation from the rear are screened off. Y Y

Now, the object of the Vpresent invention is to eliminate such disturbances in communication andltrafe as are caused by the signal reaching the receiving point several times from the same direction. Experimentshave shown that the same signal is heardltwo or g three or even more times at the receiving `the sending stations, to these different frequencies.` In so far as theA alterations in the frequency of the oscillations serving for the transmission vof the signals are concerned, either the carrier radio frequency may be altered or else,in case `of modulating frequencies, these latter may be varied. `Arrangements at the receiving station,in.accordance or BERLIN, GERMANY; A CORPORATION or MnTnon Fon -wranrnss COMMUNICATION ,y

192s. Serin Np. esaess.

with this invention, are so chosen that the I f signal transmitter -automatically changes Vits frequency at the end of each group of signal or previous to the beginning of a new group.

The numberof signals which are comprised d in one group and are transmitted at the ysame frequency depends, of course, upon the rate ofthe signal transmission, in which connection it must be kept in mind that theffirst repetition at the receiving station occurs only l/Tth of one second later. For instance,if the rate of transmission is slow'so that the duration of asi'gnal takes almost on'esseventhV of a second, then the next signal should, of.

course, be sent out at a different frequency.

In so far as the arrangements at fthe receiv-V ing end are concerned, these can be'properlyA made permanent according tothe nature of theV frequency changes land'other Voperating conditions. If at the sending "end it is not the carrier frequency itself which is varied, but rather a modulating frequency, then the. selection of the signals at the receiving station OUT) can be effected by variationof the tuning'of the selective means after rectification. Hence,

separation of the incoming signals is possible in such a manner that the frequency of the selective vcircuit isvvaried before the signal is repeated due earth. p'

Another embodiment ofthe basic idea to itsncircu'lation around the ,w

would be to "provide "different selective Vcir-` i cuits having different constant tuning, and

these could befconnected in rotation between the incoming aerialand thereceiver apparatus, this being'accomplishable by the agency of a revolving commutator or change-over switch revolving in synchronism with i the rate of change in frequency at the transmitter station` As regards the number of Vfrequen-- cies tobe employed in order to Aeliminate the said disturbances due towrecurrence or repetition of the signal, from two to three fre- V Vquencies may be supposed to be" adequate-to satisfypractical conditions and requirements,

since the intensity of the repeated signals is naturally subject to marked attenuation. y

It is `furthermore possible to leave the incoming frequency at the receiver unchanged, if heterodyne reception is resorted to, in such a Way that the frequency of the heterodyne is Y varied by the same amount as the frequency of the next signal in the transmittingstation, with the result that the ensuing beat note is unvaried. `The group of signals which has once travelled around the earth, has a difterent frequency for the next signal so that it `vvillnot be received orthat a different note will beheerd, while all consecutive signals invariably ,resultin'the same note... The specification is accompani d by draw-` ings in which Fig. 1 is a transmitter employingV fixed i tuning and mechanical switching;

Fig. 2 is a receiver similarly utilizing fixed tuningand mechanical switching; f i Fig.` 3ds a` transmitter employing variable timings' y Fig. 4 isv a` receiver arranged toicooperate with thetransmittershown in'Fig; 3; and Fig. 5 is anotherreceiver arranged tol prof' vide a constant frequency heterodyne tone.

\ `Referrin=`,; to Figurel thereare a suitable number offmastcr oscillators Y 2, permanently tuned to different recprencies. In the present case four have been indicated butptwofo three, are sufficient. The master oscillators are coupled successively toa power amplif-- flcr 4 through intermediate switching device 6, the contact` arm of which isf rotated at a nod `speed ai suz'rtable'idriviiigmechanism 8; 1 The time of duration 02Ev signals lon any onerequency is-to be one-seventlr of a second or slightly 1es`s,and the` speed orotatrono the driving` mechanism 8r is adjusted accordagLLtaIing into`r accountA the mimber'of frequencies employed. In the present 'ca-se a speed-o 1220- revolutions perI Ininute will ie- 'sult intr ai constant freqilency duration of'` once eighth of a second. The*` transmitter' may be` keyed 'either by aA key 150, `arranged to si-4 i nrultanecusl'y` key allA of the masterfosci-llators,

or by a. key l2, arranged toi bias'thecontrol electrode oit Van amplifier tube', inlrnovvn manner. The energy is radiatedover a suitable radiatingfmea'ns 14.` f

f IinFigure 12the receiver consists of a: suit,- able antenna 16, the energy collected by which is` annpliied',inE arelatively broadly tuned amplifier 18, and the-ampliiied energy is fed successively and cyclically to selective or shamply'tuned amplifiersf20reachof which 'is i tuned to a frequencycorresponding to one of the transmission frequenciesof the master 'oscillators-f2,` through' a distributing switch 22tthecontactor of'which isrot'ated by a drivingvmechanism: 24adjust`ed: tov rotate in synchronisnfr:with,` the transmitter switch. The outputstrout` the-selective amplifiers alrecombincd,uand "the signal `isto translated audibly the audible note may be provided by beating the received signal with a plurality of local oscillators 26, each of which is tuned to a frequency diieringfrom the corresponding signal frequency by the desired tone frequency, and this tone may be detected bfy a detector 28, and amplified in an `audio requency amplilier 30, and translated by teleI phones 32. i y y Referring to Figure 3'there is an oscillator tube 40,1 the electrodes of` which are coupled in regenerative fashion tothe inductances 42 and 44, in series with which there are blocky ing condensers 46, and inparallel with which there is (a iixedtuning condenser 48,1 slight` `ly varied' bya relativelysmall. variable condenser 50, the rotatable plate 52 ofwhich is rctatedbya'driving mechanism 54. If the carrier energy isf to be directly varied in frequency the energy from the oscillator thus far described may be 'radiated by a suitable antenna system. f" y the. `arrangement illustrated, however,` it` ifs proposed to vary a modulating or intel mediate frequency, and accordingly the high frequency carrier is supplied by a constant frequency oscillator '6d` If desired, the vwfiedA in anwamplier'et, andcombined in. a

detector 76? with energy from ancscillator 7 8. Thisoscillator` is preferably adjustedto the same frequency as theoscillator 60', so that the beat `frequency Vis the same as: that generated in the oscillator 4(}.Ar selective amplifier 80is arranged withY a variable condenser 50g` just' as-:ilr the transmitter, andi the rotor-52 of this condenserisrotated bythe driving mechanism 514, arranged to' rotaterin synchronism with that at: the transmitter. The output from the amplifier maybe rectiiied iii` suitable detector56-,`and amplified `ina direct; current amplifier 58, and: thereafter used `in a translatordpwhich maybea tape recorder orother suitable device' responsive to the direct currentfsig'nal energy. f

It will be understood that? whenK the trans-` mitter is so arrangedthat the oscillator' 40 provides the carrier energy directlygithe rev receiver may be varranged so that therantemia 72 feeds theenergy which it collects directly to the amplifier 80.3.vithoutsthe useo inter mediate heterodyne. 76s and/l8r f f An` alternativereceiver isi indicated in.` Fig-f ure 5, and comprises an antenna 72, an amplifier 74, a first detector 7 6 and an oscillator 78, all as Was described in connection with Figure 4. In this case, however, the intermediate frequency amplifier 82 is sufliciently broadly tuned so that an intermediate frequency corresponding to that generated by the oscillator in the transmitter is passed therethrough. The intermediate frequency energy is combined in a second detector 84 with energy from a local oscillator 86, the frequency of which is varied by a rotatable condenser 50, the rotor 52 of Which is driven by mechanism 54 arranged to rotate in synchronism with the equivalent mechanism at the transmitter. In this Way a constant frequency tone signal is obtained, which is fed I through an audio frequency amplifier 88, preferably tuned to the desired tone signal, and translated in telephones 90.

In the arrangements shown in Figures 3, 4 and 5, the speed of rotation of the variable condenser is so chosen that the generated frequency Will be repeated at intervals of time such that the original signal transmitted at like frequency will have attenuated to a negligible value, and may be for example threesevenths of a second, or thereabouts. The frequencies may vary continuously, or if it is desired that the frequency be constant for periods in the neighborhood of a seventh of a second, the rotatable plates may be so cut that this effect Will be obtained.

I claim:

1. The method of signaling in order to avoid interference of a signal with itself due to traveling along different paths to a receiver, which includes transmitting at different frequencies successive portions of the signal, and selectively and successively translating the signal portions in the order and at frequencies corresponding to those at which the signal Was transmitted, the portioning of the signal being chosen such that the time of transmission of a portion thereof precludes interference at the receiver due to reception of the same signal portion along other paths.

2. The method of minimizing interference of a signal with itself which includes transf mitting successive portions of the signal at different frequencies, synchronously and selectively collecting and translating signal energy so transmitted, the time of changeover from one frequency to another being chosen so that When signal portions arrive at the translation point along paths other than that desired, another portion of the signal is being selectively translated.

3. The method o-f avoiding interference due to the receipt of the same signal at difl ferent time intervals which includes transmitting successive portions of the signal at different frequencies Within a range of frequencies, selectively and synchronously altering the frequency of a receiver to correspond to the transmitted frequencies, thetimeof Y changeover in frequency being such that value.

FRITZ SCHROTER.

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